Workaround under Windows:
If you are running a 32-bit Android studio, you need to modify the file:
In the startup directory of Andriod Studio. Find studio.exe.vmoptions this file. Add in the back
-djava.net.preferipv4stack=true
-didea.updates.url=http://dl.google.com/android/studio/patches/updates.xml
-didea.patches.url=http://dl.google.com/android/studio/patches/
If it's 64-bit, find the Studio64.exe.vmoptions file, and add it to the back.
-djava.net.preferipv4stack=true
-didea.updates.url=http://dl.google.com/android/studio/patches/updates.xml
-didea.patches.url=http://dl.google.com/android/studio/patches/
Save.. Restarting studio generally solves the problem.
If you have a VPN or proxy, you can configure the proxy.
References for agents:
Http://www.cnblogs.com/dyllove98/archive/2013/08/04/3236884.html
This article references: http://www.inferjay.com/blog/2013/09/26/update-android-studio-fail/
Connection Server failed when Android studio was updated